DEVICE IN EXTENDIBLE CRANE BOOMS

Abstract: An extendible crane boom comprises a number of telescopic boom sections, which are each composed of a tube and a holder mounted at an outer end of the tube and serving as an attachment for a double-acting hydraulic cylinder which serves to displace the individual telescopic boom section out of or into an immediately preceding boom section so as to extend and shorten, respectively, the crane boom in its entirety. The cylinder part (7) of each hydraulic cylinder is connected to the holder via a coupling comprising a screw joint having several screws, and a pair of cooperating male and female members (11, 9), one of which has a part-spherical surface (18) which faces the other and which, when the screw joint is but loosely tightened, allows adjusting the cylinder part into a desired, correct working position in relation to the holder, in which position the screw joint (13) is finally tightened.

Description: DEVICE IN EXTENDIBLE CRANE BOOMS Technical Field of the Invention This invention relates to a device in extendible crane booms of the type which, in addition to a tubular base boom section, comprises one or more boom sections arranged telescopically within the base boom section and each composed of a tube and a holder mounted at an outer end of the tube and serving as an attachment for a double-acting hydraulic cylinder which serves to displace an individual boom section out of or into an immediately preceding boom section so as to lengthen and shorten, respectively, the crane boom in its entirety. Background Art Telescopic, extendible crane booms of the general type described above are often used as outer booms in knuckle-boom cranes. In addition to the base boom section articulated to the first boom section of the crane, they often include more than one telescopic boom section. Thus, a common crane type comprises, in addition to the base boom section, three telescopic boom sections (con- ventionally termed "extensions"), each of which is ope¬ rated by means of an associated hydraulic cylinder whose cylinder part is fixed in the above-mentioned holder and extends in cantilevered fashion inwards from the holder while the piston rod can be extended outwards from the holder, thus entraining the telescopic boom section located immediately outside. When all the telescopic boom sections are retracted in the base boom section and the crane boom has minimum length, all these hydraulic cylin¬ ders will be located close to each other adjacent the outer side of the base boom section. Then, if the cylin¬ der parts of the hydraulic cylinders are not in accurate parallel alignment with each other, they may risk to come into contact with each other or with other components of the crane boom construction, thus giving rise to abrasion and wear, and sometimes even collision phenomena. It therefore is extremely vital that the cylinder part of each hydraulic cylinder be mounted in an accurately defined, predetermined position with respect to the holder. In prior-art cranes, two alternatives to solve the above problem have been used. In one alternative, the outer side of the cylinder part has fixedly mounted thereon two diametrically opposed pins which engage in corresponding holes in side members of the holder while a bracket-like member projects from the holder a slight distance towards the free end of the cylinder part and is fixed thereto spaced from said pins, which retain the cylinder part against lateral movements while the bracket-like member retains it against movements in the vertical direction. A serious drawback of this alterna¬ tive is that the pins on the cylinder part as well as the holes in the holder require extremely meticulous and, hence, costly preparations to ensure that the cylinder part be located in the desired position parallel to the main axis of the crane boom. Also the bracket member increases the overall construction costs. Moreover, every subsequent adjustment of the position of the cylinder part is impossible. If, therefore, any cylinder part, after the crane has been used for some time, is moved out of its parallel position with respect to the crane axis, the crane boom must be dismounted and the faulty compo¬ nents exchanged. Not only is this a costly operation but it also involves considerable downtimes, during which the crane cannot be used. According to the other alterna¬ tive, the cylinder part is connected to the holder via a flanged joint comprising a flange which is mounted on the cylinder part, engages with a flat surface a correspond¬ ing flat surface on the holder and is connected there- to via a suitable number of screws. In this case too, extremely meticulous preparations are required for the flange as well as the holder, especially in conjunction with the welding of the components included in the holder. Moreover, any subsequent adjustment of the position of the cylinder part is made with the aid of washers. This is a troublesome and time-consuming work. Objects and Features of the Invention The present invention aims to overcome the above- mentioned drawbacks inherent in prior-art cranes and provide a device by means of which the parallelism between the individual hydraulic cylinder and the asso¬ ciated crane boom section can be ensured in a simple, efficient and cost-saving way. A basic object of the invention therefore is to provide a device which enables mounting the hydraulic cylinder on the associated holder without the need of any time-consuming and costly prepa¬ rations in respect of the holder and the connection com¬ ponents on the cylinder part. Another object is to pro¬ vide a device enabling subsequent adjustment of the posi¬ tion of the hydraulic cylinder relative to the holder in a simple manner. According to the invention, the above-mentioned objects are achieved by means of the features recited in the characterising clause of appended claim 1. Other features of an especially preferred embodiment of the invention will appear from the dependent claims. Brief Description of the Accompanying Drawing In the drawing, FIG. 1 is a schematic, perspective exploded view illus¬ trating the inventive coupling device between a cylinder part and a holder, and FIG. 2 is a simplified perspective view of an indivi¬ dual boom section included in a crane boom and having a holder, to which a hydraulic cylinder is connected via a coupling device according to claim 1. Detailed Description of a Preferred Embodiment of the Invention In the drawing, reference numeral 1 generally desig¬ nates a crane boom section which is composed of a tube 2 and a holder 3, schematically illustrated. The tube 2, which in this example has a hexagonal cross-sectional shape, is open at both ends in the case when the boom section is telescopic and insertable in a base boom section (not shown) of e.g. an outer boom. An inner end of the tube or the boom section is designated 4 while an outer end thereof is designated 5. The holder 3 carries a hydraulic cylinder, generally designated 6, which in con¬ ventional manner includes a cylinder part 7 and a piston rod 8. Assuming that the boom section shown in Fig. 2 is one out of several telescopic boom sections, the inner end 4 is inserted in a base boom section or a telescopic boom section located inwardly thereof, while an outer boom section of smaller dimensions can be inserted in the outer end 5 of the tube 2. This outer telescopic boom section (not shown) then is movable back and forth rela¬ tive to the tube 2 by means of the piston rod 8 of the hydraulic cylinder 6, the piston rod 8 being movable out of and into the cylinder part 7. To this end, the hydrau¬ lic cylinder 6 is double-acting. In Fig. 1, reference numeral 9 designates a female member having a seat or a seat surface 10, while 11 designates a male member. In Fig. 1, the female member 9 is schematically illustrated as a plate which in one way or another is included in the holder 3 and is a fixed part thereof. For example, the plate 9 may form part of a vertical, transverse flange included in the holder 3. The plate 9 has a plurality of holes 12 for receiving a corresponding number of screws 13. In the illustrated, preferred embodiment, the number of holes and screws is four. The male member 11 consists of a ring or a substan¬ tially annular body which encloses the outer end of the cylinder part 9 and is fixedly connected to it, e.g. via a threaded joint, optionally a thermally-glued joint or, alternatively, a welded joint. On its circumferential surface, the ring 11 has a number of projections 14 cor- responding to the number of screws and formed with inter¬ nally threaded holes 15 for the screws. The outer end of the ring 11 terminates in a sleeve-like portion 16, through which the piston rod 8 is passed and which is insertable in a central hole 17 in the female plate 9. According to the inventive principle of the inven¬ tion, the illustrated coupling device includes between the cylinder part 7 and the holder 3 a part-spherical surface 18 which in this case is formed on the male mem¬ ber or ring 11. More specifically, the part-spherical surface 18 extends from the annular sleeve portion 16 out to the circumferential surface of the annular body 11. In the mounted state of the coupling, the part-spherical surface 18 is adapted to engage the above-mentioned seat surface 10 which in this example is assumed to have a conical or truncated shape. As a result, a line contact will exist between the male surface 18 and the female surface 10, more specifically in the form of an annular or circular contact line whose radial location along the female or seat surface 10 is determined by the relation- ship between the cone angle of the seat surface and the radius of the spherical surface 18. In the case of a small radius of the spherical surface, the contact line is located close to the hole 17 whereas in the case of a relatively large spherical radius, the contact line will be located further away from the hole 17, although still in contact with the female surface 10. When the cylinder part 7 is to be mounted on the holder 3, the annular body 11 is brought into contact with the holder or the female plate 9, so that the convex part-spherical surface 18 comes into contact with the seat surface 10, and the screws 13 are initially tight¬ ened comparatively loosely in the associated threaded holes 15. In the next step, the cylinder part is aligned in a suitable manner to a position in which it is sub¬ stantially exactly parallel to the longitudinal axis of the crane boom, i.e. the centre axis of the tube 2, whereupon the screws 13 are finally tightened so as to firmly hold the cylinder part in the given position parallel to said longitudinal axis. Thanks to the part- spherical shape of the engagement surface 18, the circu¬ lar contact line between the surfaces 18 and 10 can be positioned in varying ways along the seat surface 10. This in turn means that the cylinder part 7 can be posi¬ tioned in the desired axis-parallel position even if the component 9 forming part of the holder 11 is not in exact perpendicular alignment with the longitudinal axis or if the annular body 11 does not extend exactly coaxially with the cylinder part. In other words, the holder 3 and the coupling ring 11 can be manufactured and mounted without high tolerance requirements, whereby the overall cost of the crane boom can be reduced. Another advantage of the inventive coupling device is that, when required, it allows quick and easy subsequent adjustment of the position of the hydraulic cylinder relative to the asso¬ ciated boom section. Conceivable Modifications of the Invention It is understood that the invention is not restrict¬ ed only to the embodiment described above and illustrated in the drawing. Thus, the part-spherical surface need not necessarily be formed on a ring or coupling component associated precisely with the hydraulic cylinder, but may instead be formed on the holder or any other part con¬ nected thereto. Nor does the part-spherical surface necessarily be convex. Thus, it may instead be concave and cooperate with a suitable countersurface or counter- piece. Moreover, the seat surface receiving the male member may have a shape other than conical, e.g. be part- spherical having another radius than a part-spherical and convex engagement surface on the male member. Similarly, it should be pointed out that nor the illustrated part- spherical surface on the male member or the seat surface in the female member need necessarily be coherent and annular. Thus, these surfaces may have recesses or interruptions between individual partial surfaces which together form a part-spherical or conical configuration. For reasons of manufacture, it is however preferred in practice to have continuous, annular surfaces. Also, it is conceivable to form, for example, the seat in the female member from a number of spaced-apart, suitably shaped projections, against which a part-spherical sur¬ face can be engaged to permit pivoting the hydraulic cylinder in conjunction with mounting or subsequent adjustment. According to the invention, the essential thing thus is that either of two elements of male and female design included in the coupling device has a convex or, alternatively, a concave part-spherical sur¬ face or configuration that permits pivoting the hydraulic cylinder relative to a point of articulation located substantially coaxial with the longitudinal centre axis of the cylinder.

Claims: CLAIMS 1. A device in extendible crane booms, e.g. outer booms, of the type which, in addition to a tubular base boom section, comprises one or more boom sections (1) arranged telescopically within the base boom section and each composed of a tube (2) and a holder (3) mounted at an outer end (5) of the tube and serving as an attachment for a double-acting hydraulic cylinder (6) which serves to displace an individual boom section out of or into an immediately preceding boom section so as to lengthen and shorten, respectively, the crane boom in its entirety, c h a r a c t e r i s e d in that the cylinder part (7) of each hydraulic cylinder (6) is connected to the holder (3) via a coupling comprising a screw joint having a plu¬ rality, e.g. four, of screws (13), and a pair of coope¬ rating male and female members (11, 9), one of which has a substantially part-spherical surface (18) which faces the other and which, when the screw joint (13) is but loosely tightened, permits adjusting the cylinder part (7) into a desired, correct working position in relation to the holder (3), in which position the screw joint is finally tightened. 2. A device as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the part-spherical surface (18) is convex and formed on the male member (11). 3. A device as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the male member is a ring ( 11 ) enclosing the cylinder part (7) and being fixedly con¬ nected thereto, e.g. by means of a threaded or welded joint. 4. A device as claimed in claim 2 or 3, c h a r ¬ a c t e r i s e d in that the female member (9 ) comprises a seat which is adapted to receive the part-spherical, convex male member (11) and is delimited by a concave surface (10) of substantially conical shape. 5. A device as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the part-sphe¬ rical surface (18) is annular and coherent. 6. A device as claimed in claim 4 or 5, c h a r - a c t e r i s e d in that the seat surface (10) is annu¬ lar and coherent.

Inventors: FORSBERG LARS, FORSBERG, LARS
Applicants: FORSBERG LARS, HIAB AB, FORSBERG, LARS
Application year: 1994
Main classification: B66C23
IPC codes: B66C23